An inkjet printing mechanism is a type of non-impact printing device which forms characters and other images by controllably spraying drops of ink from a printhead. Inkjet printing mechanisms may be employed in a variety of devices, such as printers, plotters, scanners, facsimile machines, and the like. For convenience, inkjet printers are used herein to illustrate the concepts of the present invention.
The printhead ejects ink through multiple nozzles in the form of drops which travel across a small air gap and land on a recording media. The drops are very small. Inkjet printers commonly print within a range of 180 to 600 dots per inch (dpi). The ink drops dry on the recording media shortly after deposition to form the desired printed images.
There are various types of inkjet printheads including, for example, thermal inkjet printheads and piezoelectric inkjet printheads. By way of example, for a thermal inkjet printhead, ink droplets are ejected from individual nozzles by localized heating. A small heating element is disposed at individual nozzles. An electrical current is passed through the element to heat it up. This causes a tiny volume of ink to be rapidly heated and vaporized by the heating element. Once vaporized, the ink is ejected through the nozzle. A driver circuit is coupled to individual heating elements to provide the energy pulses and thereby controllably deposit ink drops from associated individual nozzles. Such drivers are responsive to character generators and other image forming circuitry to energize selected nozzles of the printhead for forming desired images on the recording media.
During start-up just prior to a printing cycle, it is common to maneuver the printhead to a service station and prepare the printhead by firing ink drops into a reservoir. Sometimes hundreds, or even thousands, of ink drops are rapidly fired into the reservoir. This preliminary firing clears the nozzles and orifices of any ink build-up or debris in preparation for a more controllable ink deposition when the printhead is returned to the recording media. The printhead returns to the service station periodically while printing is in progress to re-clean the nozzles. Routine servicing is commonly scheduled once to twice per page of printing. The cleansing process helps maintain printhead reliability.
As the printhead is firing ink droplets into the reservoir, it releases undesired ink aerosol. Inkjet aerosol is small droplets of ink that are generated as a result of firing an inkjet printhead. These small droplets are often not deposited directly into the reservoir, but instead end up contaminating the printhead and the internal surfaces of the printing mechanism. The smaller the droplets, the more sensitive they are to outside influences such as air currents which aid in misdirecting the droplets away from the reservoir. Ink contamination causes additional undesired problems such as dirt build-up, high frictional forces on moving parts, and operator exposure to wet ink.
It is desirable to control the flow of inkjet aerosol in an effort to minimize the adverse effects of ink contamination.
One prior art solution to controlling inkjet aerosol is to provide an absorbent surface that is close to the printhead when firing. The aerosol impinges on this surface, and the liquid ink coalesces out of the air. This technique is not satisfactory, however, for inks that contain significant amounts of solids because the absorbent material can quickly clog. The accumulated solids continue to build up until they contaminate the printhead. The absorbent method also has limits for non-solid inks because a large volume of absorbent material must be provided to store the amount of ink discharged over the life of the printer. This makes the printer larger, more expensive, and imposes other restraints on the design.